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1. Field of the Invention
This invention relates to the use of certain ferrocene bisphosphonite ligands in the presence of a Group VIII metal to catalyze the hydroformylation of C4 to C20 conjugated dienes to alkenals. The invention also relates to composition of selected hydroformylation catalysts derived from phosphonite ligands and a Group VIII metal. The invention further relates to the composition of the phosphonite ligands.
2. Description of the Related Art
The hydroformylation of alkadienes to produce alkenals, for example the hydroformylation of butadiene to pentenals, is generally known. Pentenals are potential intermediates to a variety of useful compounds. Pentenals may be oxidized and optionally esterified to pentenoic acids or methyl pentenoates, which in turn can be hydroformylated to 5-formylvaleric acid or 5-formylvalerates. 5-Formylvaleric acid and 5-formylvalerates are useful intermediates in the production of epsilon caprolactam. Currently processes for the direct production of pentenoic acids or methyl pentenoates by carbonylation of butadiene may require high temperatures; i.e., greater than 120xc2x0 C. An advantage of hydroformylation of butadiene to pentenals is that it requires much lower temperatures; i.e., less than 100xc2x0 C.
Most processes to produce pentenoic acid or pentenoate esters involve the use of halide promoted catalysts such as described in U.S. Pat. Nos. 5,250,726 and 5,288,903. These processes have the disadvantage that they use high concentrations of hydrohalogenic acids and other rigorous conditions, which necessitate cost-increasing measures in connection with safety and the corrosion of the equipment. In U.S. Pat. No. 5,028,734 issued Jul. 2, 1991, a process is described for the selective carbonylation of a conjugate diene by contacting with carbon monoxide in the presence of a hydroxyl group-containing compound such as methanol. This catalyst system is less corrosive than the process that is described in U.S. Pat. Nos. 5,250,726 and 5,288,903 but still has the disadvantage of requiring the use of a catalyst consisting of palladium, a bidentate phosphine and an acid to catalyze the transformation of butadiene to pentenoate esters. The main disadvantage of the presence of an acid is its reactivity towards the alcohol and the bidentate phosphines used in the process. Alcohols will react with the acid promoter to produce esters and phosphines will be converted to phosphonium salts. The combination of these two factors renders the invention described in U.S. Pat. No. 5,028,734 non-practical from an industrial point of view.
Pentenals may be alternatively hydrogenated to pentenols, which upon hydroformylation give hydroxyhexanals. 6-Hydroxyhexanal is a useful intermediate in the production of epsilon caprolactone.
Pentenals may be alternatively hydroformylated to dialdehydes, including adipaldehyde. Adipaldehyde is a valuable intermediate which is potentially useful in the production of compounds such as adipic acid (by oxidation), hexamethylenediamine (by reductive amination), and 1,6-hexanediol (by hydrogenation). Production of adipaldehyde by hydroformylation of pentenals would be a desirable improvement over current processes based on the oxidation of cyclohexane because it is based on butadiene, a less expensive feedstock.
Although a variety of complexes of bis(phosphorus) ligands with rhodium catalyze the hydroformylation of butadiene, the selectivity for 3- and 4-pentenals is low for many of them. Various publications in the 1970""s and 1980""s, describe hydroformylation of butadiene catalyzed by rhodium complexes with monodentate phosphines (For example, Fell, B. and W. Rupilius Tetrahedron Lett. 1969, 2721-3; Fell, B. and W. Boll Chem.-Ztg. 1975, 99, 452-8; Fell, B., W. Boll, and J. Hagen Chem.-Ztg. 1975, 99, 485-92; Fell, B. and H. Bahrmann J. Mol. Catal. 1977, 2, 211-18). These systems yield primarily valeraldehyde because the rhodium/phosphine catalysts are also very efficient catalysts for hydrogenation. Van Leeuwen reported that under mild conditions (95xc2x0 C. and 175 psi, (1.2 MPa), 1:1 H2/CO) rhodium complexes of bidentate phosphines also yield primarily valeraldehyde (European Patent No. EP33554 A2, Van Leeuwen, P. W. N. M. and C. F. Roobeek J Mol. Catal. 1985, 31, 345-53). Recently, however, Ohgomori reported that under more vigorous conditions (100xc2x0 C. and 1300 psi, (8.9 MPa), 1:1 H2/CO) these catalysts give 3-and 4-pentenals (Ohgomori, Y., Suzuki, N., and Sumitani, N. J. Mol. Catal. 1998, 133, 289-291). However, under these conditions the pentenals undergo further hydroformylation to a mixture of dialdehydes, lowering the yield. It has also been reported that hydroformylation of butadiene under biphasic conditions using the sulfonated phosphine P(C6H4-3-SO3Na)3 yields 3-pentenal (B. Fell, P. Hermanns, and H. Bahrmann, J. Parrot. Chem., 340 (1998), pp. 459-467, German Patent No. DE 19532394).
A recent series of patents (U.S. Pat. No. 5,312,996, U.S. Pat. No. 5,817,883, U.S. Pat. No. 5,821,389, European Patent No. 872,469, European Patent No. 872,483, U.S. Pat. Nos. 5,892,127, 5,886,237, and European Patent No.872,483) discloses a hydroformylation process in which rhodium complexes of bidentate phosphite ligands catalyze the hydroformylation of butadiene to 3-pentenals. U.S. Pat. No. 5,710,344 discloses the use of rhodium complexes of bidentate phosphorus ligands wherein the ligand contains a bridging group bonded through Pxe2x80x94O bonds to a pair of trivalent phosphorus atoms with the other two bonds to each phosphorus being either a pair of Pxe2x80x94N bonds (phosphorodiaminites), a pair of Pxe2x80x94C bonds (phosphinites) or one Pxe2x80x94N and one Pxe2x80x94C bond (phosphoroaminites).
These prior art processes using rhodium complexes of bidentate phosphorus ligands to produce 3-pentenal from butadiene have various disadvantages. For example, the isolation of 3-pentenal in these systems is complicated by side reactions such as isomerization to 2-pentenal, reduction to valeraldehyde, and further hydroformylation to a mixture of dialdehydes. Thus, these catalysts do not give high selectivity to 3-pentenal at high conversions of butadiene. For example, the highest selectivity reported for a rhodium complex of a bis(phosphite) ligand is 84% at 37% conversion of butadiene (U.S. Pat. No. 5,886,237). The bis(phosphinite) ligands disclosed in U.S. Pat. No. 5,710,344 disclose up to 95% selectivity at 95% conversion of butadiene, but only in the presence of greater than 5 equivalents of the bis(phosphinite) ligand.
Although bidentate phosphonite ligands are not commonly used in catalysis, they have been employed as catalysts for a variety of transformations, including nickel-catalyzed cyclotrimerization of alkynes (Heterocycles, 1997, 44, 443-457), nickel- and palladium-catalyzed alkylations and cross couplings (J. Org. Chem. 1995. 60, 2016-2; J Chem. Soc., Perkin Trans. 1, 1995, 17, 2083-96), nickel-catalyzed hydrocyanation of olefins (U.S. Pat. No. 5,523,453), and rhodium-catalyzed enantioselective hydrogenation of olefins (Reetz, M., Gosberg, A., Goddard, R., Kyung, S.-H.. Chem. Commun. 1998, 19, 2077-2078).
Bidentate phosphonite ligands based on a ferrocene backbone have been disclosed in U.S. Pat. No. 5,817,850 (see Fig. A below) and Chem. Commun. 1998, 19, 2077-2078. The bidentate phosphonites described in these publications have biphenol or binaphthol derived terminal groups that are bridged. U.S. Pat. No. 5,817,850 discloses a hydrocarbonylation reaction of an alkene with carbon monoxide and hydrogen to form an aldehyde which is catalyzed by a transition metal complex of the bridged terminal group containing ferrocene bis(phosphonite) disclosed therein. 
(X is alkylidene, S, Se, or a direct bond)
Furthermore, while the catalyst systems described above may represent commercially viable catalysts, it always remains desirable to provide even more effective, higher performing catalyst precursor compositions, catalytic compositions and catalytic processes to achieve full commercial potential for a desired reaction. The improvement in effectiveness and/or performance may be achieved in any or all of rapidity, selectivity, efficiency or stability.
The successful hydroformylation of conjugated dienes and/or selectivity for linear aldehyde products are particularly desirable attributes.
The invention provides for a bidentate phosphonite ligand having the structure represented by the following Formula I: 
wherein the Ar groups are either the same or different unbridged organic aromatic groups such as substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, mixtures thereof or the like. It should be appreciated that for purposes of this invention the above structural formula is illustrative of the staggered configuration of phosphonite ferrocene; i.e., (xcex75-C5H4P(OAr)2)Fe, but is not intended to be limiting. As such the eclipsed configuration as well as rotational variations thereof are to be considered intrinsically equivalent to the illustrated staggered configuration as generally known in the art.
The present invention further provides for a hydroformylation process comprising the steps of reacting an ethylenically unsaturated compound with CO and H2 in the presence of a catalyst composition comprising a Group VIII metal or Group VIII metal compound and phosphonite ligand having a structure represented by Formula I and thus producing an aldehyde. The invention is especially directed to a hydroformylation process involving the reaction of a conjugated C4 to C20 diene with CO and H2 in the presence of the catalyst composition.
The invention also provides for certain bidentate phosphonite ligands and catalyst compositions made therefrom useful in hydroformylation processes. In particular, these include the combination of a ligand of Formula I with a suitable Group VIII metal or Group VIII metal catalyst precursor.